Streamwise and Vertical Dispersal of Tracer Stones in an Equilibrium Bed
Streamwise and Vertical Dispersal of Tracer Stones in an Equilibrium Bed
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DOI：
10.1029/2022wr033137
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发表时间：
2022-11
影响因子：
5.4
通讯作者：
E. Viparelli;Amanda Balkus;D. Vázquez‐Tarrío;K. Hill;M. Tal;J. Fedele
中科院分区：
文献类型：
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作者：
E. Viparelli;Amanda Balkus;D. Vázquez‐Tarrío;K. Hill;M. Tal;J. Fedele
与表征河床淤积和退化的时间间隔相比，模拟不均匀沉积物在短时间间隔内的运移、侵蚀和沉积仍然是一个悬而未决的问题，因为河床物质负荷和冲积沉积物之间的泥沙通量的量化很复杂。Parker， Paola和Leclair在2000年提出了一个形态动力学（PPL）框架来克服这个问题。这个框架在这里被用来模拟砾石示踪剂在三种不同环境下的扩散，一个实验室水槽，一个山间小溪，和一个辫状河。为了简化问题，(a)假定河床坡度、河床输运速率和河床形态在空间和时间上都是恒定的（平衡），(b)泥沙夹带和沉积采用恒定步长公式，(c) PPL框架采用一维（横向平均）模型。与实验室实验相对照的模型验证表明，随着水流输送能力的增加，沉积物携带的最大高程比密度可能在沉积物中向下迁移。模型结果与现场数据的对比表明，平衡解能较好地反映示踪剂的扩散。平衡模型还可以根据短期床层水平变化的幅度，重现一块示踪剂在流向上的亚扩散和超扩散。最后，示踪剂在横截面上的平均高程随着时间的推移而降低，因为埋在沉积物深处的颗粒很少被重新带入层状输运。
Modeling transport, erosion, and deposition of nonuniform sediment over temporal intervals that are short compared to those characterizing channel bed aggradation and degradation remains an open problem due to the complex quantification of the sediment fluxes between the bed material load and the alluvial deposit. Parker, Paola, and Leclair in 2000 proposed a morphodynamic (PPL) framework to overcome this problem. This framework is used here to model the dispersal of a patch of gravel tracers in three different settings, a laboratory flume, a mountain creek, and a braided river. To simplify the problem, (a) the bed slope, bedload transport rate, and bed configuration are assumed to be constant in space and time (equilibrium), (b) sediment entrainment and deposition are modeled with a constant step length formulation, and (c) the PPL framework is implemented in a one‐dimensional (laterally averaged) model. Model validation against laboratory experiments suggests that, as the transport capacity of the flow increases, the maximum elevation‐specific density of sediment entrainment may migrate downward in the deposit. The comparison between model results and field data shows that the equilibrium solution can reasonably capture tracer dispersal. The equilibrium model can also reproduce subdiffusion and superdiffusion of a patch of tracers in the streamwise direction, depending on the magnitude of the short‐term bed level changes. Finally, the average tracer elevation in a cross‐section decreases in time because particles that are buried deep in the deposit are only rarely reentrained into bedload transport.